So I checked a few things.

My SD card was a Kingston 16 GB Class 10, rated for 45MB/sec.  It should be OK.

The power adapter was a Samsung unit rated at 2A at 5V.   I replaced it with a unit rated at 2.4A at 5.25V.

I rewrote the SD card.  I used gparted to resize the root partition to be the remainder of the space on the card.  It was 3.2GB with 2.3 GB used.  Now it is ~12GB with 2.3 GB used.  I wanted to resize the swap partition, which is set to 488 MB.  For some reason gparted wouldn't let me touch it.  

I rebooted and reinitialized things.  It runs much, much faster, but it still seems slow.  Each package upgrade in #dnf upgrade is probably taking a minute now, versus 5 minutes before.